America is not the only country in the world that has televised debates between political leaders and last night Mark Pack at Liberal Democrat Voice had a pop at the Guardian for ignoring the fact that there are other countries in the world that do the same, some of which have political systems that are more similar to Britain's than the American one is.

But there is a reason why Gordon Brown, David Cameron and Nick Clegg should look to the US if they want to know how the forthcoming debates are going to pan out. It's simple: we just know much more about the American debates. Much more that has been written about the presidential debates, and what impact they have on elections, than about similar contests in places like Australia, Canada and Sweden.

So, what are the lessons for the three leaders? I can think of five.

1. Expectations matter — a lot.

This is true of many political situations (eg byelections) but it is particularly true of television debates. The standard trick is to play down expectations, so that a competent performance becomes a success. George Bush tried this before he debated John Kerry in 2004 and Barack Obama tried it before he took on John McCain in a "town hall" debating format last year.

According to Obama's campaign manager David Plouffe (who has just published a book about the 2008 election), the Obama camp described McCain "as the best town hall performer in the history of American politics". I expect that within the next few weeks we'll hear someone from Labour – probably Lord Mandelson – conceding that Cameron is likely to win the UK debates because he's a more polished television performer than Brown.

Cameron's problem is that this is true. In some respects the Tory leader may find it hard to "win" the debates whatever he does because many in the commentariat are already taking victory for granted.

2. Television debates are about character as much as policy.

Elections aren't just popularity contests and the debates will be about policy, and not about whether candidates prefer The X Factor to Strictly Come Dancing. But the most memorable moments in American presidential debates have been those that have provided a vivid insight into character. Debates are a test of emotional intelligence. According to Drew Westen (who analysed debates extensively in his book The Political Brain), "we are not moved by leaders with whom we do not feel an emotional resonance".

The classic example of this came in 1992, when Bill Clinton was debating George Bush. A woman in the audience asked the candidates how "national debt" had affected them personally. She meant "recession", but Bush did not pick up on this and he did not understand the question. Even after the moderator explained what she intended to say, Bush was still flummoxed and he waffled about a meeting that he had attended recently in a church.

After much struggle, it was Clinton's turn – and he did something quite extraordinary. He took three steps toward the woman and he asked her, "Tell me how it's affected you again?"The woman was speechless. Clinton helped her along, describing some of the terrible economic stories he'd heard as governor of Arkansas. But the words weren't as important as the body language. The three steps he had taken toward the woman spoke volumes about his empathy, his concern, his desire to respond to the needs of the public. Bush, by contrast, was caught gazing at his wristwatch – hoping desperately that this awkward moment would soon be done.And, indeed, it was. The presidential campaign was, in effect, over.

3. Some of the best lines are the ones that are spontaneous.

Candidates prepare endlessly for televised debates, and they should. But they also need the wit to be able to come up with a spontaneous response, and the confidence to use it without worrying that it has not been tested in advance. One of Ronald Reagan's best debate moments came in the 1984 head-to-head with Walter Mondale when he declared: "I will not make age an issue of this campaign. I am not going to exploit, for political purposes, my opponent's youth and inexperience."

That was effective, and clearly rehearsed. But it probably wasn't as influential as the moment in 1980 when he depicted Jimmy Carter as a windbag with the spontaneous put-down: "There you go again."

4. The media can be wrong about the winner.

After televised debates journalists like to declare who won. But different audiences respond to debates in different ways and the political commentators cannot always predict how ordinary voters will respond. In his book on the Obama campaign, Plouffe says this happened all the time when Obama was fighting Hillary Clinton in the primaries.

"The voters generally gave us higher marks than the pundits, and gave Clinton lower marks than the pundits. This proved quite meaningful as the primary wore on," he wrote.

5. Most debates probably won't make much difference.

At the risk of spoiling the fun, it's worth repeating a point made by my colleague Michael White; these events may not make any difference at all. In the US some presidential debates may have been influential. But most of them weren't. Kerry was deemed to have won all his encounters with Bush in 2004, but that did not help him on polling day. Although no one can predict the future, the most likely scenario is that the Tories will start the election campaign ahead in the opinion polls – and that three televised debates later they will still be in front.